1. Field of the Invention
The present invention relates to a medical device. More particularly, the present invention relates to a medical device used for a medical prosthesis and an artificial tissue which are implantable and tissue-regenerative, such as a pledget, a bolster, a patch graft, a suture,-wound and burn dressings, a donor-site skin graft, a post-operative antiadhesive, an artificial blood vessel, an artificial urethra, an artificial ureter, an artificial esophagus, an artificial trachea, an artificial membrana tympani, and an artificial oral mucosa.
2. Description of the Related Art
In the field of surgery, when damage, abnormality, dysfunction or the like occurs in a certain site of body tissue, the defective tissue is conventionally and frequently repaired by anaplerosis and prosthesis using an artificial substance as a medical device substituting the function of the tissue, for curing the tissue, preventing adhesion of the tissue and restricting the abnormal development of the tissue. The above-mentioned medical devices are required to have: biocompatibility in blood, biological fluid and/or body tissue; physical properties such as strength, elongation, softness and flexibility, and chemical and biological safety necessary for the portion and condition to be applied and suture and anastomosis; and suitable operativeness.
Generally, existing tissue-derived materials, whether homologous or heterologous, are conventionally used because of their acceptable safety and efficacy characteristics, even though undesirable conditions such as immunological rejection, blood coagulation, tissue hypertrophy, keloid or the like may be caused in some cases when enthesis is conducted. The tissue-derived materials include medical devices derived, for example, from human cerebral dura mater, human fascia lata, horse pericardium and pig pericardium.
On the other hand, synthetic polymer materials are also widely used as medical devices because such materials have excellent physical properties which can be easily controlled. However, many of the synthetic polymer materials are inferior to the aforementioned tissue-derived materials in terms of biocompatibility, bioaffinity and the like. Moreover, these synthetic polymer materials lack physiological function, for example, tissue regeneration. Therefore, the synthetic polymer materials merely substitute the body tissue with foreign substances. Thus, a novel medical device possessing the above-mentioned excellent characteristics is still required.
As medical devices made of such tissue-derived materials or synthetic polymer materials, the following materials have been conventionally developed.
For examples Japanese Patent Publication No. 3-4229 relates to a medical prosthesis utilizing human amnion. U.S. Pat. No. 4,361,552 relates to a burn dressing in which a crosslinked human amnion is used.
Furthermore, Japanese Patent Publication No. 58-52662 relates to a structure for covering damage made of an air permeable cloth substrate on which collagen-dispersed gel is carried. Japanese National Publication No. 61-502129 relates to a collagen-based biodegradable matrix for use in the topical application of an external or internal wound.
However, none of the above-mentioned medical devices described in the publications sufficiently satisfies all of the above required properties. The above-mentioned medical devices satisfy only a specific property among biocompatibility, strength, flexibility, operativeness for operation, but they do not satisfy the other properties such as biocompatibility, strength, flexibility and operativeness. Otherwise, even though some of the above-mentioned medical devices may possess all properties to a certain level, the levels are insufficient for each of the required properties.
More specifically, for example, human amnion described in Japanese Laid-Open Patent Publication No. 3-4229 comprises cells and cytoplasm such as an epithelium layer and a fibroblast layer. Therefore, there is a possibility that serious side-effects are caused due to the activity of a slow virus, the activity of prion which is a pathogen causing Creutz feldt-Jakob syndrome and an immunological rejection. If the human amnion is sufficiently crosslinked, for example, by glutaraldehyde to decrease these medical risks and to improve the properties of material, the modified human amnion cannot be absorbed in the body, and as a result, a foreign substance is present in the body such as the case of TEFLON.TM. (polytetrafluoroethylene). Thus, chemically modified materials are disadvantageous in that the materials permanently remain in the body and are further encapsulated by surrounding tissue, and the encapsulated tissue portion is thickened and enlarged with the elapse of time. Consequently, disadvantageous disorders, such as adhesion between the peripheral tissues are caused. In this way, the above-mentioned conventional medical devices are not medical devices for homologous transplantation.
A medical prosthesis made of a human cerebral dura mater, which has cell tissues, has been used for several decades, and is accepted as a medical prosthesis for homologous transplantation. However, it is not legally accepted to be applied to a biological region except for the human cerebral dura mater. Moreover, it has been recently reported that a serious side effect, that is epilepsy, occurs after the prosthesis on human cerebral dura mater. Furthermore, since the medical prosthesis made of a human cerebral dura mater is collected from a human body, the material is disadvantageous in its poor ability of supply and extremely high cost. Thus, the medical prosthesis made of a human cerebral dura mater has a critical defect that it is not equally offered in terms of medical welfare.
When a defective part undergoes anaplerosis or prosthesis by exsection in an abdominal organ, it is impossible to suture the defective part as it is in the case where the organ is a feeble organ such as the liver. On the other hand, when a defective part undergoes anaplerosis or prosthesis by exsection in a bone, significant strength is required to suture and fix the defective portion. In such a case, a suture reinforcing material excellent in strength and flexibility is required.
Thus, a medical device, which is excellent in strength, softness and flexibility and has bioabsorption ability, is required. For example, a mesh fabric made of polyglycolic acid is used as a medical device satisfying the above conditions. However, since the mesh fabric is permeable, it disadvantageously leaks body fluid, for example, bile from a gallbladder, from an organ to which the mesh fabric is applied.
In prosthetic therapy of an affected portion, a medical device is required to satisfy the following conditions: capability of preventing liquid and gas in the applied portion from being leaked and lost; easiness to be sutured; capability of reinforcing by suture; bioabsorption to promote regeneration and self-repair of tissue of an affected part; excellent biocompatibility; excellent operativeness, for example, easiness to treat in surgical operations in terms of adhesion to a defective part; stably supply at reasonable cost.